1. Field of the Invention
The present invention relates to an image processing technique, and more particularly, to a technique for removing noise from an image that is represented by digital data.
2. Description of the Related Art
Conventionally, a smoothing filter is generally used in a process for removing noise of an image that is represented by digital data.
For example, Japanese Patent Publication No. 2000-069291 discloses a technique for preventing an image from being degraded by changing the characteristic of an applied smoothing filter according to the characteristic of input image data.
Additionally, for example, Japanese Patent No. 3165225 discloses a technique for removing extraneous noise by applying a noise removal filter (smoothing filter) only to a portion of a low luminance level, which is significantly influenced by extraneous noise applied to a luminance signal, in luminance to density conversion.
However, with the noise removal techniques using such smoothing filters, noise removal is made by performing a process such as a process for replacing the level value of an observed pixel with an average of the level values of neighboring pixels. Therefore, there is a problem that the image obtained using that process is degraded in resolution, and, namely, the image becomes a “blurred” image.